כו עַל–כֵּן קָֽרְאוּ לַיָּמִים הָאֵלֶּה פוּרִים עַל–שֵׁם הַפּוּר עַל–כֵּן עַל–כָּל–דִּבְרֵי הָאִגֶּרֶת הַזֹּאת וּמָה–רָאוּ עַל–כָּכָה וּמָה הִגִּיעַ אֲלֵיהֶם
26. Therefore, they called to these days “Purim” from the name “pur.” Therefore, because of all of the words of this letter, and what they saw on such, and what happened to them…
According to the Alshich, the Sanhedrin of Mordechai’s day named the holiday.